The present invention relates to multi-cylinder internal combustion engines of the type comprising:                an air delivery pipe adapted to convey air to each engine cylinder,        at least one intake valve for each cylinder that controls the communication between said pipe and the combustion chamber of the respective cylinder, and                    wherein each intake valve is controlled by actuator means for making a particular quantity of air flow into said combustion chamber, said actuator means being susceptible to controlling the respective intake valve independently from the other cylinders and according to a variable actuation method,                        injector means for each cylinder adapted to carry out the injection of a determined quantity of fuel into said combustion chamber,        electronic control means adapted to control:                    said actuator means, for adjusting the opening time and stroke of the respective intake valve,            said injector means, for adjusting said determined quantity of fuel,wherein, when the engine is subject to an operating variation request from a first operating condition to a second operating condition, said electronic control means are adapted to select the cylinder to which said second operating condition is assigned based on a programming delay.                        
International application no. WO02/073020 offers a method, for an internal combustion engine with variable actuation of the cylinder valves, for managing the operating variations wherein, in correspondence with the request for a new torque, an actuation of the injector and the valves is performed according to intermediate modes between the old mode and the new mode, until the injector and the valves can eventually be actuated in a cylinder according to the new mode.
Therefore, said method envisages an immediate variation of the cylinder operating modes, as a result of the request for a new torque, in order to reach the new mode in the cylinders as soon as possible, but gradually.
European Patent Application no. 07425773.4 of the same Applicant describes a multi-cylinder internal combustion engine with independent cylinders wherein a control mode is envisaged for the injector and the valves whereby, as a result of a variation in the engine operating mode, the electronic control means estimate the quantity of air and fuel corresponding to the new operating mode, estimate the actuation times of the injector and the valves corresponding to the estimated quantity of air and fuel and, based on said actuation times, they assign the new operating mode to the first cylinder being able to actuate it. Particularly, based on the actuation times, the electronic control means estimate the delay, with respect to the moment when the calculation of said times is made, in order to reach top dead centre in a cylinder for the implementation of the combustion process corresponding to the operating condition of the new operating mode of the engine; said electronic control means also assign said operating condition for the first time to the cylinder which, after the moment when the calculation of said times is made, is first susceptible to finding itself in a top dead centre condition for the implementation of a combustion process after said delay has passed.
The above-indicated solution, therefore, envisages that the internal combustion engine responds to the torque variation requests, assigning the new operating conditions for the first time to a cylinder which firstly, following an engine operating variation request, is effectively able to satisfy such new operating conditions. The cylinders implementing a combustion process before the cylinder to which the new operating mode is assigned, continue to operate in the old mode.
Hence it is clear that the solution under discussion, similarly to the solution described in International Application no. WO 02/073020, following a torque variation request, does not envisage an immediate response of the engine according to the actuation of the valves and the injectors in intermediate modes; but, it checks which cylinder is first able to actuate the new operating modes in order to assign said modes to it.
The main aim of the solution proposed in European patent application no. 07425773.4 was to ensure a fast response of the engine to the operating variation request, at the same time obtaining excellent combustion process in the cylinders. In the solution of International application no. WO02/073020, the intermediate modes that are actuated in the cylinders generate combustion processes that are far from being excellent and that hence considerably reduce the performance of the engine.
However, the Applicant has recently noticed that the solution of European patent application no. 07425773.4 has some drawbacks that will become clear as follows.
FIG. 1 represents an operating diagram of an internal combustion engine as described in European patent application no. 07425773.4, in the presence of a (load or speed transient) variation of the engine conditions.
Herein, the actuation diagrams of the respective injector means and the respective intake valve are shown for both the cylinders CIL1 and CIL2, as also for the electronic control means, for an operating period identified by the time axis.
In the first operating mode of the engine both the cylinders operate in the same operating conditions characterised by the actuations indicated in the figure as INJ(0) and EV(0), respectively of the injector means and the intake valve. From FIG. 1 it can be understood that the programming delay corresponding to the first operating mode is equal to three engine strokes.
In line with the torque variation requested, the electronic means evaluate the times necessary for the actuations of the intake valve and the injector means, adapted for establishing the combustion process corresponding to such new required torque.
The electronic control means, hence, calculate the programming delay corresponding to the new operating conditions of the cylinders and based on this it evaluates to which cylinder to assign the operating condition corresponding to the new conditions.
The programming delay corresponding to the new operating condition of the example in FIG. 3 is equal to four engine strokes.
As has been schematically represented in FIG. 1, for cylinder 2 it is not possible to carry out the combustion process adapted to generate the new torque requested in correspondence with its top dead centre condition for the implementation of a combustion process. In fact, from FIG. 1, it can be understood that starting from the moment of the new torque request, only three engine strokes follow before reaching such top dead centre condition of cylinder CIL2, whilst the actuation delay of the new operating conditions is equal to four engine strokes.
The time available, starting from the moment of the new torque request, in order to reach the top dead centre condition in cylinder CIL2 for the implementation of a combustion process is, hence, insufficient to actuate in synchrony the injector means and the intake valve of that cylinder in order to establish the new operating conditions.
In other words, as schematically indicated in FIG. 1 the actuations, and specifically the actuation stage of the injector means, adapted to establish a combustion process able to generate the requested torque, should have started before the torque request time. This condition is schematically represented in FIG. 1 by the part relative to the actuation of the injector means of the cylinder CIL2 which is indicated as eliminated by a prohibition sign.
It emerges, hence, that it is in particular the necessary time for the new injection operations that determines the unsuitability of cylinder CIL2 to be the first cylinder to operate according to the new operating conditions.
Whereas, it emerges that the cylinder CIL1, on the other hand, is the first cylinder susceptible to operating according to the new operating conditions. In fact, starting from the moment of the new torque request until the top dead centre condition of the cylinder CIL1 for the implementation of a combustion process, four engine strokes follow each other, which correspond exactly to the necessary time for implementing the new operating conditions.
Following the evaluations described above, the electronic control means assign to the injector means and the actuator means of the cylinder CIL1 intake valve, the actuation modes corresponding to the new operating conditions. In FIG. 1, these new actuation modes are respectively indicated as INJ(−1) and EV(−1). The arrow represented in FIG. 1, which is laid out transversally, indicates the fact that once the electronic means have verified that the CIL2 is not susceptible to being the first cylinder to operate in the new operating conditions, they automatically assign to the actuator means and the injector means of the cylinder CIL1 such new actuation modes.
The actuation modes of the injector means and the actuator means of the intake valve of the cylinder CIL2, and hence the operating conditions of the latter, are controlled in such a way that they continue to be the same as those preceding the torque increase request. Such actuation modes are respectively indicated in brackets by INJ(OLD) and EV(OLD) and are the same as the modes INJ(0) and EV(0) previously defined.
Following the last cycle carried out by the cylinder CIL2 in the old operating conditions (with the actuation modes INJ(OLD) and EV(OLD)), the electronic means finally assign to the latter the operation with the new operating condition for which the actuation modes associated with this are the modes INV(−1) and EV(−1)).
Since the programming delay of the new operating conditions is increased by one engine stroke with respect to the previous activation delay, the electronic means start to operate the control for the implementation of the new operating conditions on the various cylinders one stroke before the stroke in which the electronic means intervened in the old operating conditions. Such intervention variation is indicated schematically in FIG. 1 using horizontal arrows, for both the cylinders CIL1 and CIL2, in line with the strokes in which they operate in the new operating conditions.
The Applicant has checked that the control strategy described above can determine situations in which the combustion process is not susceptible to being controlled in a predetermined way. The main cause is due to the complicated handling of the electronic control means, which, according to such control strategy, must continuously check in real-time the actuation delays of the valves and injector with respect to each operating mode.
For determined engine loads and speeds, such activity of the electronic control means may be inefficient. In fact, despite the control means operated to identify the very first cylinder that might operate in the new operating modes, in actual fact, it is not possible to guarantee deterministic and predictable behaviour during arbitrary manoeuvres made by the driver. Thereafter, depending on the individual case the cylinder to be actuated first in the new operating mode may be different, and the combustion process that is triggered in such first useful cylinder might be different from the best one envisaged, or may, in particular, differ from the best one in an unpredictable and uncontrollable way.
Furthermore, a considerable load increase corresponds systematically to the contemporary handling of two programmings on different cylinders, as described in FIG. 1. One of the two cylinders, particularly that being unable to actuate the new torque request (CYL2 in FIG. 1), is systematically programmed with the old reference. This behaviour, acceptable for occasional abrupt load reference variations, becomes difficult to manage if it is desired to fully exploit the possibility, offered by technology, of varying the load reference, even abruptly, systematically and with the aim of differentiating the torque delivered by each cylinder.
Furthermore, processing the above-indicated control strategy requires complex and highly performing software determining high production costs.
In view of the above-indicated drawbacks, the Applicant offers a new solution for the control of the transients of an internal combustion engine, according to the independent claims from 1 to 6.
Unlike the proposals of the above-discussed solutions, wherein control systems are envisaged that evaluate in real-time how and when to adopt the new operating conditions of the cylinders, in the various ways described above, in the present invention a programming delay is fixed a priori for each operating condition during the set-up stage of the control means, depending, exclusively on the speed values of the engine. This means that in correspondence with a particular engine speed, the programming delay associated with it is always the same, irrespective of the new conditions requested.
The fact that the programming delay is artificially defined depending only on the speeds, allows its value to be evaluated a priori at the corresponding speed and to be stored in the electronic control unit in such a way that it is always available.
The programming delay following a request determines when each operating condition must be programmed in order to be actuated in the cylinders. Therefore, according to the present invention, from the moment of the operating mode variation request the control system is able to identify, based on such a programming delay, the cylinder to which the new condition is to be assigned, and the moment in which it will be actuated for the first time in the cylinders, without having to carry out any real-time processing.
The innovative approach of the control system according to the present invention is therefore clear and, as emerges from the above, it differs from the solutions developed up to now in the approach of the solution to the problem, that is leaving a real-time control of the transients from one engine operating mode to another, providing, on the other hand, a means of handling these transients according to a simplified pattern chosen a priori.
As will be clear below, this choice allows the control system to be simplified to a large extent, above all allowing the complications of the feedback controls, that are absolutely necessary in the systems of the above-indicated art, to be abandoned.